Interpretive Summary: The lack of novel strategies to enhance the immunogenicity of subunit vaccines to induce protective immunity against many infections of poultry hinders rapid progress in developing recombinant peptide vaccines against diseases to which effective vaccines are not available yet. In this paper, ARS scientists collaborated with scientists from a private industry to evaluate a novel adjuvant formulation which was designed to enhance cell-mediated immunity. As a model recombinant vaccine antigen, these authors used a profilin antigen which is a highly conserved protein that is present on all apicomplexa parasites including coccidia. To demonstrate the efficacy of this new adjuvant-vaccine formulation, QCDCRT-profilin complex was injected into young chickens and they were challenged with live coccidia parasites later. The results provided first evidence that the immunization of young chickens with QCDCRT-profilin complex induced better protection against coccidiosis in terms of enhanced body weight gain and lower gut damage. Furthermore, chickens which were vaccinated with this novel adjuvant-vaccine complex demonstrated significantly enhanced protective immune parameters. These results will help poultry industry to better design novel recombinant vaccines against complex diseases like coccidiosis.

Technical Abstract:
The effects of two novel adjuvants, QCDC (Quil A/cholesterol/DDA/Carbopol) and QCDCRT (QCDC/Bay R1005/cytosine-phosphate-guanosine oligodeoxynucleotides, CpG) emulsified with profilin, a conserved Eimeria recombinant protein, against avian coccidiosis were determined in broiler chickens. Chickens were subcutaneously immunized with isotonic saline (control), profilin (P), profilin emulsified with QCDC (P-Q), or profilin with QCDCRT (P-QR) at 2 and 9 days post-hatch and orally challenged with 1.0 × 104 sporulated oocysts of E. acervulina (EA) at 7 days post-immunization. All profilin-immunized groups showed increased body weight gain compared with the control group, and the P-QR group treated with CpG had significantly higher body weight gain than those of the P and P-Q groups following EA challenge infection. All groups immunized with profilin showed significantly decreased intestinal lesions compared with the control group with the P-QR group showing the lowest intestinal lesions among the profilin-treated groups. Finally, the P-QR group showed greater CD4+/CD8+ and TCR1+/TCR2+ splenocytes, and higher anti-profilin serum antibody titers compared with the P and/or P-Q groups following EA challenge infection. These results further suggest that vaccination of chickens with profilin in combination with the QCDCRT adjuvant would provide a novel control strategy against EA infection in commercial flocks.